The present invention relates to an oil level detector for use in an oil tank of a vehicle to detect the level of oil, and more particularly to such an oil level detector which has means to effectively prohibit oil from passing to its inside.
FIG. 4 illustrates an oil level detector according to the prior art. This structure of oil level detector comprises a flat, circular holder base 5 having a tube 52 at the bottom side and a top block 51 at the top side, a top cover 6 covered on the top block 51, a float 53 mounted around and moved vertically along the tube 52, a detecting circuit board 8 mounted in the bore 521 of the tube 52, and a screw cap 7 mounted with a rubber ring 71 and threaded into the inner thread 522 at the bottom end of the tube 52. The lead wires 81 of the detecting circuit board 8 are extended out of a hole 511 at the top block 51 and a hole 61 at the top cover 6, and connected to power source. This structure of oil level detector is still not satisfactory in function. Because oil may permeate through the gaps between the inner thread 522 of the tube 52 and the threaded periphery of the screw cap 7, the detecting circuit board 8 tends to be damaged by oil leaked in the tube 52. Further gas or moisture may permeate through the holes 61,511 to the inside of the tube 52 to damage the detecting circuit board 8. There is known a similar oil level detector in which the tube which holds the detecting circuit board on the inside is a close-end tube directly injection-molded from plastics. Because the bottom end of the tube is a closed end, oil is prohibited from leaking in the tube. However, the plastic material property of the tube will be damaged a certain period of time after dipping in oil, causing oil to leak in the tube through damaged structure of the tube.